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path: root/key/key.go
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// Package key implements signify key format
package key

import (
	"bytes"
	"crypto/rand"
	"crypto/sha512"
	"encoding/binary"
	"errors"

	"golang.org/x/crypto/ed25519"
)

// DefaultRounds of KDF
const DefaultRounds = 42

var (
	ErrInvalidPK  = errors.New("unsupported format")
	ErrInvalidKDF = errors.New("unsupported KDF")
	ErrInvalidKey = errors.New("invalid key")
	ErrKeyNum     = errors.New("verification failed: checked against wrong key")
	ErrInvalidSig = errors.New("signature verfication failed")
)

var (
	pkAlg  = [2]byte{'E', 'd'}
	kdfAlg = [2]byte{'B', 'K'}
)

// Deriver returns a derived key from passphrase
type Deriver interface {
	Derive(salt []byte, rounds int, length int) ([]byte, error)
}

// Generate a new key pair
func Generate(der Deriver) (*Pub, *Sec, error) {
	pubKey, secKey, err := ed25519.GenerateKey(rand.Reader)
	if err != nil {
		return nil, nil, err
	}

	// secret key
	sec := &Sec{PKAlg: pkAlg, KDFAlg: kdfAlg}
	copy(sec.Key[:], secKey)

	checkSum := sha512.Sum512(secKey)
	copy(sec.Checksum[:], checkSum[:len(sec.Checksum)])

	if _, err := rand.Read(sec.Salt[:]); err != nil {
		return nil, nil, err
	}
	if _, err := rand.Read(sec.KeyNum[:]); err != nil {
		return nil, nil, err
	}

	// Pbdkf
	if der != nil {
		xor, err := der.Derive(sec.Salt[:], DefaultRounds, len(sec.Key))
		if err != nil {
			return nil, nil, err
		}
		for i := range xor {
			sec.Key[i] ^= xor[i]
		}
		sec.KDFRounds = DefaultRounds
	}

	// public key
	pub := &Pub{PKAlg: pkAlg, KeyNum: sec.KeyNum}
	copy(pub.Key[:], pubKey)

	return pub, sec, nil
}

func unmarshal(data []byte, v interface{}) error {
	buf := bytes.NewReader(data)
	if err := binary.Read(buf, binary.BigEndian, v); err != nil {
		return err
	}
	return nil
}

func marshal(v interface{}) ([]byte, error) {
	buf := new(bytes.Buffer)
	if err := binary.Write(buf, binary.BigEndian, v); err != nil {
		return nil, err
	}
	return buf.Bytes(), nil
}